Objective. Although somatic symptoms are common among mental health patients, their association with symptom severity and inpatient treatment outcomes is not yet well understood. Methods. Using a pre-post design and latent class analysis (LCA), 641 inpatients (63.4% female) were classified based on their self-reported somatic symptoms. We examined how the resulting somatic symptom classes related to depression and anxiety symptom severity pre-treatment (T1) and to symptom reduction post-treatment (T2). Results. Our results suggest four somatic symptom classes, namely (1) unspecific/low somatic symptom burden, (2) sexual problems, (3) gastrointestinal symptoms with pain syndrome, and (4) cardiopulmonary symptoms. While class 1 indicated the lowest pre-treatment depression and anxiety symptom severity, class 2 reported high depressive symptoms coupled with low anxiety, class 3 reported moderate depressive and anxiety symptom severity, and class 4 reported the highest depressive and anxiety symptom burden. Somatic symptom classes, however, did not predict the degree of reduction in either depression or anxiety symptoms post-treatment. Conclusions. These findings demonstrate somatic heterogeneity in mental health patients and reveal the relationship of somatic symptom patterns to affective symptom severity. Clinical implications are discussed.